This invention is directed to admixtures for hydraulic cement compositions and more particularly to water-reducing admixtures capable of increasing the slump of hydraulic cement compositions without excessive retardation of the cement setting time.
Various water-reducing admixtures for hydraulic cement compositions are known. These admixtures are capable of modifying cement slurry compositions to permit the use of lesser amounts of water to achieve a desired plasticity or workability. Alternatively, these admixtures can be used to provide increased plasticity or workability, as compared to a cement composition without the admixture added, at the same water/cement ratio. The admixtures also provide higher compressive strength in the cement composition after setting, due either to the use of less water in the mix or to a more complete dispersion of the cement particles in the plastic cement mix.
Lignosulfonic acid salts and salts of aromatic sulfonic acid-aldehyde condensate polymers are well known water-reducing agents. In general relatively high dosages of these water-reducing agents are necessary in order to obtain significant water-reduction. However, such dosages generally enhance the rate of slump loss and tend to excessively retard or prevent setting.
Various polyhydroxy compounds, such as glucose, gluconic acid salts, glucoheptonic acid salts, and various polysaccharidic materials, have also been proposed for use as water-reducing agents. However, these materials generally suffer from the disadvantage of imparting unacceptably high levels of set retardation to the cement composition with an accompanying reduction in strength gain.
There is accordingly a continuing desire in the art to develop new water-reducing admixture compositions which can provide a high degree of fluidity to hydraulic cement compositions without undue adverse effect on the cement setting time.